I really wouldn't recommend using ISO higher than 800 on K7 for best detail.
But if I were you, I would care less about the settings and more about boxing as a sport.
Good sport photographers see that magic moment way before we "normal" people do, because they know where to look and what to expect. For example, there is no way you can get exclusive shots of Rafael Nadal, if you haven't fully analized his unique play style.
If you are serious about shooting boxing, learn (and practise) this sport as much as you can. Find a fighter that you like, analize his fighting style, meet him in person and learn about his personality.
I believe that is a better advice, than saying that K7 produces an unpleasing amounts of noise at higher ISO's
Wish you the best and hope to see some breathtaking pics soon